Method and apparatus for electrostatic separation



1, I938. T. BANTZ ET AL 2,105,865

METHOD AND APPARATUS FOR ELECTRCSTATIC SEPARATION Feb.

Filed March 1, 1955 Patented Feb. 1, 1938 METHOD AND APPARATUS FOR ELECTED STATIC SEPARATION Theodor Bantz, Frankfort-on-the-Main-Praunheim, Georg Grave, Frankfort-on-thc-Main- Heddernheim, and Erich Oppen,

Hanover- Kirchrode, Germany, assignors to American Lurgi Corporation, New York, N. Y., a corporation of New York Application March 1, 1935, Serial -No. 8,934

' In Germany January 31, 1935 4 Claims. (01. 209-127) This invention relates to a method and apparatus for electrostatic separation.

It is known that electrostatic separation is difficult when the size of the particles to be sep- 5 arated is below a certain value. Now, it is made possible by the present invention electrostatically to separate particles of such minute size.

The drawing represents diagrammatically an example of the invention. The material to be treated, e. g. a mixture of pyrite and quartz, is

taken from a hopper 2 and.- delivered at a regulated rate by the slide 3 to the feeder drum l and falls to the inclined plate 4 of sheet-iron or the like. -It is found that the particles of pyrite for example reach a higher velocity on this plate than the quartz particles, because the latter are attracted by the plate on account of the electric charge thereon produced by the friction and thus move at a slower rate compared with the other particles. By this means it results that the pyrite particles fall into the receptacle 1 and the quartz particles into the receptacle 6. An ex- The electric charge carried by the particles varies with their electrical conductivity. The showering of the mixture onto the plate 4 tends to break up agglomerates of particles and thus to facilitate the separation.

. When, treating certain mixtures, for example ores, the effect can be increased by arranging a second plate 8, for instance of sheet-iron, above plate 4. The better effect may be explained by the fact that the pyrite particles which also carry a small electrical charge are attracted byv the plate 8. It is advantageous to ground the plate 4, for instance of usual sheet-iron, so that the quartz particles are lifted from the plate as little as possible. It was found that the efiect is by far inferior and ceases altogether, in case the plate 4 is charged electrically. Thus, with the process according to the invention no foreign source of electricity is needed, but the particles of the material produce their electricity themselves by friction.

Since the treatment according to the invention comprises the efiect of the frictional electricity the shape of the surface 4 is not without importance. A certain roughness of the surface has proved advantageous. For instance the efiect is better when using ordinary sheet-iron instead of smooth tin plate. In some cases a'non-conductor may be employed for plate 4 instead of sheet-iron. The surface 4 can be plane as drawn;

but it is also possible to use a curved surface instead, the peripheral surface of a cylinder for example.

Further, it became evident that the angle of separation can be enlarged in order to obtain a 5 better separation by the use of auxiliary planes '9 and I0, whichit is advantageous to ground. The particles which are electrically charged by friction are attracted more intensively, after leaving the planes 4, by the planes 9 and I0 respectively, thus explaining the better efiect observed.

We claim:-

1. Process for the electrostatic separation of mixtures of finely divided conductive and nonconductive particles which comprises dropping the same from a height onto an inclined, conductive, uncharged plate thereby breaking up agglomerates, allowing said particles to slide along said plate and off the edge thereof whereby the conductive particles are thrown a greater distance beyond the edge of the plate in a horizontal direction than the non-conductive particles, and separately collecting the particles with reference to the distance to which they are thrown in a horizontal direction.

2. Process as defined in claim 1 in which the plate is grounded.

3. Apparatus for the electrostatic separation of finely dividedmaterial comprising an inclined conductive uncharged plate, means for showering the material from a considerable height onto said plate adjacent the higher edge thereof, means adjacent the lower edge of the plate for separately collecting the particles falling over the edge of the plate and a second un- 3 charged plate arranged above and substantially parallel to said inclined conductive uncharged plate.

ductive uncharged plate.

'l'I-IEZODOR' BANTZ. GEORG GRAVE. ERICH OPPEN. 

